/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.io.network.partition;

import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Set;

/** A basic queue with duplicated elements ignored during {@link #add(Object)}. */
public class DeduplicatedQueue<T> {
    /** The major component to store elements. */
    private final Queue<T> queue = new LinkedList<>();

    /**
     * Saves the same elements as {@link #queue}, but helps to deduplicate elements at constant time
     * complexity.
     */
    private final Set<T> set = new HashSet<>();

    /**
     * @return true if this queue did not already contain the specified element
     */
    public boolean add(T t) {
        if (set.add(t)) {
            queue.add(t);
            return true;
        }

        return false;
    }

    public T peek() {
        return queue.peek();
    }

    public T poll() {
        T t = queue.poll();
        set.remove(t);
        return t;
    }

    public void remove(T t) {
        if (set.remove(t)) {
            queue.remove(t);
        }
    }

    public Iterable<T> values() {
        return queue;
    }

    public boolean isEmpty() {
        return set.isEmpty();
    }
}
